1. Statement of the Technical Field
The invention concerns fluid working, and more particularly systems and methods for wrapping fluid flow in a fluid working apparatus, for example an expander or compressor, which results in an increased capacity to perform work by the fluid or on the fluid.
2. Description of the Related Art
A turbo-expander is a machine which continuously converts kinetic energy into mechanical energy by harnessing the pressure and heat of pressurized fluid to rotate a shaft. FIGS. 1 and 2 show an exemplary axial turbo-expander 10. Each stage of the expander 10 includes a rotatable rotor 12 and a stationary stator 14. Inlet vanes 16 and outlet vanes (not shown) may be provided to help guide the path of the flowing fluid and the vanes may serve as the stator for one or more of the stages. The rotors 12, stators 14 and vanes are supported in a housing 18. To ensure proper flow and rotation, each of the rotors 12 must be manufactured within tight tolerances relative to the housing 18. As illustrated by the arrows, the fluid passes through each stage a single time, interacting with the rotor 12 and stator 14 for only the period of time it takes for the fluid to pass through the stage. As the fluid passes through a given stage, the fluid expands and exerts a force to rotate the rotor 12, which in turn rotates the shaft (not shown).
Turbo-expanders are utilized in various applications, for example, a compressor-drive, power generator, brake drive, or cooling system. In the first three examples, the power transmitted to the shaft is used to drive a compressor, drive an electrical generator or is dissipated through an oil brake or air brake, respectively. In a cooling or refrigeration system, the gas exiting the expander, which is colder and lower-pressure than it was when it went in, is directed to a heat exchanger. Expanders and compressors may comprise or take on many different physical configurations, all of which are easily found in literature. The axial flow example shown provides the most useful architecture for the purpose of contrasting the difference. These applications are for illustrative purposes only and are not intended to be limiting.
An axial compressor works just like the turbo expander but in reverse. Power is supplied to the shaft which in turn rotates the rotors. The rotors accelerate the fluid and the stators diffuse the flow to obtain a pressure increase. That is, the diffusion in the stator converts the velocity increase gained in the rotor to a pressure increase. As with the expander, the fluid passes through each stage a single time, interacting with the rotor and stator for only the period of time it takes for the fluid to pass through the stage.